The field of the invention is power sources employing electrochemical cells.
Electrochemical power sources are known to employ electrochemical cells that utilize particulate electrodes. A particulate electrode generally is comprised of a bed of electrochemically active particles, or particles onto which electrochemically active material can be electrodeposited. The particulate electrode may be used in a cathodic process such as the electrodeposition of metals onto the particles, or it may be used in an anodic process such as the dissolution of metal to produce electrical energy.
Electrochemical power sources using the anodic process include, but are not limited to, metal/air batteries such as zinc/air and aluminum/air batteries. Such metal/air batteries employing an anode comprised of metal particles fed into the cell and dissolved during discharge are often called refuelable batteries. Zinc/air refuelable battery cells are comprised of an anode, a cathode, and an electrolyte. The anode is generally formed of zinc particles immersed in electrolyte and can be held in place by a mesh or honeycomb of inert conductor. The cathode is generally comprised of a semipermeable membrane, a mesh of inert conductor, and a catalyzed layer for reducing oxygen that diffuses through the membrane from outside the cell. The cathode and anode are generally separated by an electronic insulator that is permeable to the electrolyte. A zinc/air refuelable battery consumes zinc particles and oxygen to produce electricity and reaction products. The reaction products are generally comprised of dissolved zincate and particles of zinc oxide suspended in the spent electrolyte.
Metal/air refuelable batteries can be refueled in minutes or seconds, compared to the several hours typically required for recharging conventional batteries. This makes refuelable batteries very suitable for use in mobile applications such as electric vehicles, lawnmowers, portable power sources, and many other applications where rapid refuelability is desirable.
During the refueling operation, fresh electrochemically active particles, such as aluminum or zinc pellets, and electrolyte are added to the refuelable battery, and spent electrolyte containing reaction products is removed. Typically, the spent electrolyte containing the reaction products can then be regenerated.
The reaction products from aluminum/air refuelable batteries must be either transported to a major industrial facility (such as an alumina plant) for recycling or used, as is, for another purpose (such as water treatment). The spent electrolyte containing reaction products from zinc/air refuelable batteries can be completely regenerated at a much smaller facility at higher efficiency. For this reason, and also due to its lower parasitic corrosion rate, zinc may be preferable over aluminum as the anodic fuel in metal/air refuelable batteries for potential commercial applications. However, the higher energy density of aluminum may make it more suitable for some applications, especially if further advances are made in reducing its parasitic corrosion rate.
Several methods for refueling metal/air refuelable batteries have been proposed by others. One such method includes a refueling system for a zinc/air refuelable battery in which hoppers above each cell are hydraulically filled from a zinc-forming apparatus by a high-velocity jet of electrolyte passing across the top of each hopper. This and other hydraulically refueled systems have the drawback that they require a large recirculation of electrolyte to achieve complete refueling, as well as close proximity to an apparatus for storing or forming the zinc fuel. This makes them unsuitable for many applications, such as lawnmowers and portable power sources, which are impractical to return to a service site for each refueling.
Another method involves a honeycomb sheet of inert conductor that is filled with a slurry of fine zinc particles, electrolyte, and additives to form a planar anode cassette. The battery is refueled by replacing these cassettes (one cassette per cell). Such a system has the rather severe disadvantage of requiring the replacement of a large number of cassettes (for example, 528 in an electric van). Even for a small application such as an electric lawnmower, such a system would require the replacement of perhaps 24 or more individual cassettes during each refueling operation. Additional drawbacks to such a system include less than 100% utilization of the zinc and potential exposure of the user to the caustic electrolyte, which is typically potassium hydroxide.
Other refuelable battery designs employ a storage hopper above each cell for containing a reserve of metal particles, but do not adequately address the problem of how the particles and fresh electrolyte can be conveniently, reliably, rapidly, and accurately fed into the multiple storage hoppers without exposing the user to the caustic electrolyte. These and other designs also do not adequately address the problem of safely, rapidly, and conveniently removing the spent electrolyte and reaction products from the battery cells.
Thus, it is apparent that a more convenient, safe, and rapid refueling method and apparatus is needed for metal/air refuelable batteries. This is especially the situation if metal/air refuelable batteries are to be practical for powering small devices such as electric lawnmowers and portable equipment. In particular, it would be advantageous if a refuelable battery system included transportable containers capable of feeding more than one electrochemical cell. It would be further advantageous if the refuelable battery system did not allow exposure of the user to the caustic electrolyte at any time, especially during the refueling operation and during the replacement and refilling of the transportable containers. Finally, it would be advantageous if the transportable containers could be conveniently, safely, and rapidly refilled at an apparatus for storing or forming the metal fuel.